Method of chemical treatment for zinc of zinc-iron alloy surfaces

ABSTRACT

Zinc or zinc-iron alloy surfaces are treated with aqueous solution containing bichromate (Cr2O7 ) ions, nitrate (NO3 ) ions, tripolyphosphate (P3O10 ) ions, organic acid ions and surface active agent at pH 0.3-1.5 and in the treatment the surfaces are polished and have corrosion resistance.

United States Patent Nakaaki Oda Takaoka-shi;

Nagaharu Morioka, Takaoka-shi; Akira Yoshida, Tonami-shi; Yoshio Makino, Takaoka-shi, all of Japan Oct. 8, 1969 Sept. 21,1971

Nippon Soda Co., Ltd.

Tokyo, Japan Inventors Appl. No. Filed Patented Assignee METHOD OF CHEMICAL TREATMENT FOR ZINC 01R ZINC-IRON ALLOY SURFACES 8 Claims, No Drawings us. C1 156/20, 134/28, 134/29, 134/41, 252/794 rm. c1 C23g 1/02,

[ 13,oo7,4s3

[50] Field ofSearch 134/3,41, 28, 29; 156/118, 20; 252/792, 79.4, 79.5

[56] References Cited UNITED STATES PATENTS 3,060,071 10/1962 Kinder 156/18 3,524,817 8/1970 Roy et a1 134/41 X Primary Examiner-William A. Powell Attorney-George B. Oujevolk ABSTRACT: Zinc or zinc-iron alloy surfaces are treated with aqueous solution containing biclhromate (Cr O ions, nitrate (NO ions, tripolyphosphate (P O ions, organic acid ions and surface active agent at pH 0.3-1.5 and in the treatment the surfaces are polished and have corrosion resistance.

MlE'llllilUlD Ull CHEMICAL TREATMENT FOR ZINC 01R fillNC-llltflhl ALLOY SURFACES DETAILED EXPLANATION OF THE INVENTION This invention relates to a method of chemical treatment for zinc or zinc-iron alloy surfaces and l particularly for hot dip coating zinc or zinc-iron surfaces to give polished surfaces with corrosion resistances.

it has long be known that there are many uncoated spots, grazes, abrasions on zinc surfaces and the defects of the coating with zinc deteriorate corrosion resistant or gloss of zinc surfaces. It has heretofore been proposed to improve the defects by treating zinc surfaces with concentrated chromate aqueous solution including a little amount of sulfuric acid, nitric acid, hydrochloric acid or hydrofluoric acid. In such conventional treatment, only zinc surfaces may be polished and made to be corrosion resistant. However, zinc-iron alloy surfaces, which lie under zinc surfaces and come to the surface by mechanical crack or scratch of zinc surfaces or by the defects of coating with zinc, turn dark and a difference of the luster in appearance between zinc surfaces and zinc-iron alloy surfaces become large. It has also bee attempted to treat zinc surfaces, which have zinc-iron alloy surfaces on it, with aqueous solution containing phosphate ions corresponding to 0.5-2.0 weight percent of phosphoric acid and one member selected from the group of chromate ions corresponding to 0.5-3.0 weight percent of chromic acid and nitrite ions corresponding to 0.1-0.4 weight percent of sodium nitrite at pH 1.3-3.8. However, the treatment can not give entirely satisfying results, for example, the treating solution shows little polishing effect and not only zinc-iron alloy surfaces but also zinc surfaces turn into pale yellow and are easily corroded by continue out dipping for 10 days in 5 percent sodium chloride solution.

Accordingly, it is the object of this invention to overcome the aforementioned problems and disadvantages. It is another object of this invention to provide a method in which both zinc surfaces and zinc-iron surfaces are simultaneously made to be corrosion resistant.

It is another object to provide a method in which even and glossy surfaces can be gained.

It is another object to provide a method in which zinc sur-' faces having defects of dip coating such as uncoated spots, grazes, abrasions, burnt deposits and rough deposits are uniformly treated without spotting or striping.

It is another object to provide a method in which zinc or zinc-iron alloy surfaces are given good adhesive property for paints. It is another object to provide a method in which luster of zinc or zinc-iron alloy surfaces are durable.

Other objects and advantages of this invention will further become apparent hereinafter.

In our invention zinc or zinc-iron alloy surfaces are treated with aqueous solution containing bichromate (Cr O,") ions at a rate of 36-290 gJJL, corresponding to about 49-395 gJl. of potassium bichromate or 33.3-268.5 g./l. of chromium trioxide nitrate (NO ions at a rate of 4.1-41 g./l., corresponding to 42-42 g./l. of nitric acid, tn'polyphosphate (P O ions at a rate of 07-21 g./l., corresponding to about l-30 g./l. of sodium tripolyphosphate, organic acid ions and surface active agent at pH 0.3-1.5 for 10-180 seconds at about l0-50 C. and more preferably for 30-60 seconds at about 25-35 C. and pH 0.5-l.3 and then, the surfaces are rinsed with water and dried by heating or by air.

Under pH 0.3 of the treating aqueous solution good luster on zinc-iron alloy surfaces cannot be gained and above pH 1.5 zinc and zinc-iron alloy surfaces will be coated with thin chromate film and after a continuous treatment, in the case when the acidity of the treating aqueous solution become lowered by consumption of the ingredients and the solution gets many various impurities or foreign elements from treated articles, bichromate ions, nitrate ions or other necessary ingredients can be added into the treating aqueous solution in order to keep it in the indicated compositions and pH ranges and many various impurities or foreign elements carried from treated articles into the aqueous solution have little influence on the effects of the treatment.

Cations have no influence on the effects of the treatments, however potassium (K) ions at a rate of 1.3-26.6 g./l. have a effect to diminish the amount of the zinc dissolved into the treating aqueous solution to less than one-half of the amount of dissolved zinc which stands at in the absence of potassium ions.

In the treatment, dipping or spraying may be employed and any article, to the extent that it has zinc or zinc-iron alloy surfaces, such as galvanized iron sheet, goods made with zinc base alloy or zinc goods, can be successfully treated. As for the agents, ordinary grade agents on the market can be employed.

ln the preferred embodiment of the invention, treating aqueous solutions are prepared by adding chromium trioxide at a rate of 30-200 g./l., 60 percent nitric acid solution at a rate of 5-50 ml./l., sodium tripolyphosphate at a rate of 1-30 g./l., potassium bichromate at a rate of 5-l00 g./l., a little amount of salts of organic acid and surface active agents.

Chromic anhydride or chromium trioxide may be used as the source of bichromate ions and various slats such as potassium bichromate, sodium bichromate and ammonium bichromate may be also used as bichromate and potassium bichromate is preferably used as the source of bichromate ions and potassium ions.

lripolyphosphate has effects to polish only when it is used in the presence of bichromate ions and nitrate ions in spite that it is not almost effective when it is used in the absence of either bichromate ions or nitrate ions.

As, for organic acid ions many organic acids or salts, such as formic acid, oxalic acid, tartaric acid, citric acid, propionic acid, acetic acid and potassium or sodium salts thereof are used as the source of organic acid ions. and as for surface active agent polyoxy ethylene alkyl ether, polyoxy ethylene alkyl phenol, polyoxy ethylene fatty ester, polyoxy ethylene sorbitan fatty acid ester, polyoxy ethylene alkyl amine or polyoxy ethylene amide may be used and they contribute to diminishing the dissolution of zinc and smoothing zinc or zinc-alloy surfaces.

The advantages of this invention are numerous.

Zinc surfaces and zinc-iron surfaces are equally polished and show no difference in appearance and treated zinc or zinc-iron surface have tough resistance against corrosion.

The following examples are illustrative.

EXAMPLE 1 Hot dip coated steel pipes (16 mm. in diameter and 300 mm. in length) having some scratches and defects of coating on the surface was degreased with 3 percent sodium hydroxide (NaOH) aqueous solution at 70 C. for 30 seconds and then pickling with 3 percent phosphoric acid (H PO aqueous solution at 70 C. for 5 seconds.

The steel pipe after dressing was dipped in a bath of aqueous solution having the following composition at 30 C. for 30 seconds.

A composition of the bath mo, 70 g.

K,Cr,O-, 40 g. pH0.7 HNO (60%) 20 ml.

Sodium acetate 2 g.

Surface active agent 0.05 g.

(polyoxy ethylene alkyl phenol) Water L000 rnl.

After the treatment, the steel pipe was rinsed with water and dried. Beautiful metallic luster could be gained on both surfaces of zinc and zinc-iron alloy and defects of the surface became almost invisible.

EXAMPLE 2 Example I was repeated except using a bath of aqueous solution having the following composition at 30 C. for 60 seconds.

A composition of the bath CrO 50 g.

K,Cr,0 30 g. pH 0.9 HNO (60%) 15 ml.

Sodium acetate l g.

Surface active agent 0.05 g

(polyoxy ethylene alkyl phenol) Water 1,000 ml.

Beautiful metallic luster could be gained as it could be gained in Example 1.

EXAMPLE 3 Example l was repeated for nonspangle galvanized iron sheet. Corrosion resistance was extremely improved and beautiful metallic luster could be gained.

CORROSION TEST 1 Hot dip coated steel pipes (16 mm. of diameter and 300 mm. of length) were dipped in 50 percent aqueous solution of sodium chloride at 30 C. and an untreated pipe was corroded within a day and a treated pipe in Example 1 stood for 30 days and at 31th day three points of pitting could be detected but the gloss of the surfaces were almost maintained.

A pipe treated by a conventional process described in the following was at first corroded in the part of zinc-iron alloy surfaces within days and the corrosion spread all the surfaces of the pipe for days.

The conventional process.

Article was dipped for 20 seconds at room temperature in the first bath having the following composition;

CrO; 200 g. HNO (60%) 40 ml. HF (50%) 30 ml. H,so, (98%) 10 ml. Water 920 ml.

and was dipped in the second bath containing 50 g./l. of CrO at room temperature for 20 seconds.

CORROSION TEST 2 5 percent aqueous solution of sodium chloride was sprayed to hot dip coated steel pipe.

As for a treated steel pipe in Example 1, pitting occurred after hours and as for an untreated steel pipe pitting occurred after 10 hours.

CORROSION TEST 3 A sheet of galvanized iron was tested by weather-o-meter. After a continuous irradiation for 700 hours the gloss of the surfaces did not fall off.

What we claim is: I l. A method of chemical treatment for zinc or ZlflC-ll'Ol'l alloy surfaces which comprises treating said surfaces with aqueous solution containing bichromate (Cr O,) ions, nitrate (NO ions, tripolyphosphate (P O, ions, organic acid ions and surface active agent at pH 0.3-1.5.

2. A method of chemical treatment for zinc or zinc-iron alloy surfaces which comprises treating said surfaces with aqueous solution containing bichromate (Cr O ions at a rate of 36-290 g./l., nitrate (NO ions at a rate of 4.l-4l g./l., tripolyphosphate 0 0 ions at a rate ofO.7-2l g./l., organic acid ions and surface active agent at pH 0.3-1.5.

3. A method according to claim 2 in which potassium (K') ions are employed at a rate of l,3-26.6 g./l.

4. A method according to claim 2, in which potassium (K') ions are employed at a rate of l.3-26.6 g./l. and chromium trioxide is used as a source of bichromate ions and potassium bichromate is used as both source of potassium ions and bichromate ions.

5. A method according to claim 2 in which articles having Zinc surfaces are dipped in the said aqueous solution for 10-180 seconds at l0-50 C.

6. A method according to claim 2 in which the articles having zinc surfaces are dipped at about 30 C. for 30-60 seconds.

7. A method according to claim 2 in which a organic acid or a salt thereof selected from the group of formic acid, oxalic acid, tartaric acid, citric acid, propionic acid, acetic acid and potassium or sodium salt thereof is employed.

8. A method according to claim 2 in which nonionic surface active agents is employed. 

2. A method of chemical treatment for zinc or zinc-iron alloy surfaces which comprises treating said surfaces with aqueous solution containing bichromate (Cr2O7 ) ions at a rate of 36-290 g./l., nitrate (NO3 ) ions at a rate of 4.1- 41 g./l., tripolyphosphate (P3O10 ) ions at a rate of 0.7- 21 g./l., organic acid ions and surface active agent at pH 0.3- 1.5.
 3. A method according to claim 2 in which potassium (K ) ions are employed at a rate of 1.3- 26.6 g./l.
 4. A method according to claim 2, in which potassium (K ) ions are employed at a rate of 1.3- 26.6 g./l. and chromium trioxide is used as a source of bichromate ions and potassium bichromate is used as both source of potassium ions and bichromate ions.
 5. A method according to claim 2 in which articles having zinc surfaces are dipped in the said aqueous solution for 10- 180 seconds at 10*- 50* C.
 6. A method according to claim 2 in which the articles having zinc surfaces are dipped at about 30* C. for 30- 60 seconds.
 7. A method according to claim 2 in which a organic acid or a salt thereof selected from the group of formic acid, oxalic acid, tartaric acid, citric acid, propionic acid, acetic acid and potassium or sodium salt thereof is employed.
 8. A method according to claim 2 in which nonionic surface active agents is employed. 